Why you almost never wear a size 43.5 in running and trail shoes.
Clarity in the confusion
Why you sometimes have 1/3 size
Why half sizes do exist outside the EU
Table of contents
What's the deal with those half sizes?
Anyone who has ever bought trail shoes knows the moment: you try on size 39 — just a little too small. Then you take 40, and it feels just a little too big. “Do you also have 39.5?”
The short answer: no.
The long answer: half sizes do not exist in Europe. And that's not because manufacturers are lazy, but because system works differently.
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📏 European shoe sizes: 2/3 per step
In Europe we use it Parisian points system, whereby 1 size = 2/3 centimeter (about 6.67 mm).
That means:
Size 39 → 26.0 cm
Size 40 → 26.7 cm
Size 41 → 27.3 cm
So there is always 2/3 cm difference between two sizes. In the US and UK they use a different system where the step is smaller (1/3 size)That's why you see half measures there like 9, 9.5, 10, 10.5, and so on.
If you translate that into European sizes, you get something like:
US 9 = EU 42.1
US 9.5 = EU 42.7
US 10 = EU 43.3
In other words: European sizes run not in whole numbers, but in jumps of 2/3. Only each brand rounds it off just a little bit differently.
👟 Why some brands seem to have half sizes
Brands like Salomon, NNormal and The Sportiva all work with European sizing, but express it differently.
For example, Salomon and NNormal use 39 1/3, 40, 40 2/3, 41 1/3, etc. That's actually how it should be.
Other brands like Altra and Saucony simply show whole numbers, but their “EU 40” may actually be 40.3.
Brands like La Sportiva make it a bit more complicated and often have European half sizes. There's less difference between shoes there.
So even though there is no half size on the shoe — the there is a difference. Only not visible on the label.
🏔️ Summary: There's no such thing as half measures (but there is a little bit of that too)
✅ European sizes go in steps of 2/3 cm
✅American sizes have 1/3 steps (half measures)
✅ Brands round off, so 39.5 just becomes 40
✅ Always look at the length in cm (or the US size), not the number
So the next time you ask if there is a half size bigger is — you know: You already have it. It just has a different name.
Dirk
Founder of Trail.NL He's done a lot of running. From all kinds of mud runs to ultra-trails and from the well-known road marathons to hour-long runs. He's tested a lot of shoes and other gear.
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